1. Field of the Invention
The present invention relates to systems for connection of agricultural implements to tractors and particularly tool bar implements, especially those which include trailing lift assist units. More particularly, the present invention relates to a compact flexible system for connection of an agricultural implement to the three-point hitch of a tractor. The system includes a resiliently yieldable member which allows flexing between the tractor and the implement and yet provides for application of adequate down-pressure force to the implement from the tractor hitch when the implement is lowered for penetration into the ground.
2. Description of the Prior Art
A variety of systems for connection of trailing implements to a wheeled tractor have been developed in which the trailing implement is connected to the tractor by use of a conventional so-called three-point hitch. The lower links or arms of such hitches are driven by the hydraulic system of the tractor to provide operator-controlled lifting and lowering movement and forces to the attached implement. The upper or stabilizing link of these systems typically is used when the hitch system must maintain a particular, e.g. generally horizontal, pitch orientation of the implement and when the hitch system is used to transmit a positive down-pressure force to tillage tools or the like mounted on trailing portions of the attached implement.
During implement usage or when the implement is being lifted and transported, a number of forces are developed on the three-point hitch, the implement and the lift support member. The three-point hitch can provide upward lift by actuation of the power lift features of the lower support arms of the hitch. For example, the upward force is utilized for lifting and carrying the implement during transport from one location to another. During usage of the agricultural implement for tillage, the lift arms lower the implement and the combination of links, including the top link, and orient the implement in pitch to assure proper ground penetration of the tools. This often requires application of rearward compressive forces by the upper link. In ridge tillage systems, for example, pitch orientation force often is required on the implement to assist in forcing the tillage tools of the implement into the ground.
Many such implements also include a trailing wheeled lift assist support system. This is most common in heavy implements where it would be impractical or even impossible to carry the full weight of the implement in cantilever fashion on the tractor hitch system. Such trailing lift assist support systems typically include support members pivotally attached to the main frame of the implement, with one or more ground contact wheels or the like mounted on each support member behind the implement. A power lift means such as a hydraulic lift cylinder normally is included for actuation from the hydraulic system of the tractor when it is desired to transfer a portion of the weight of the implement to the trailing support system. The rear wheeled lift assist supports act in concert with the three-point hitch by selectively providing upward lift on the implement. This includes, of course, the situation where the implement tools are to be lifted clear of the ground, such as for turning at the end of a field or for transport. However, it will be appreciated that in this condition, the tractor and trailing implement constitute a rather long rigid system, from the front wheels of the tractor to the trailing support wheels.
Thus, while in the lifted position, the entire system of the tractor and trailing lift assist support members act as a fixed body with the implement carried in between the two units. During movement in this lifted position, however, the tractor may be tilted in pitch with respect to the rear lift support member as the combination passes over uneven terrain. The system therefore preferably allows for flexing as the tractor and rear wheeled lift support member pass over uneven ground.
Similarly, when the implement is being used in engagement with the soil, flexibility in pitch is important when traversing uneven ground, though perhaps not as critical. In that circumstance, the rear support assist mechanism normally is not activated and thus is free-floating, thereby resulting in a shorter effective length of the rigid system. Similar considerations apply with implements which do not include trailing lift assist means. While flexibility thus is important, the system must also provide pitch orientation with enough compressive force to maintain the tools in desired penetration of the ground.
Various arrangements of linkages have been proposed for providing yieldable interconnections between three-point hitches and the trailing frames of implements. However, most such systems are not adapted for tool bar types of implements, i.e., where a plurality of relatively independent tool gangs are attached to a transverse tool bar and are vertically movable relatively independent of one another within the range of their operative engagement with the soil. Such gangs typically trail the tool bar and have integrated down-pressure means on each gang unit. Application of orientation forces on the tool bar from the tractor remains desirable in many such instances to control and selectively increase or decrease the effective down-pressure forces across all of the individual gang units. However, there is no integrated frame rearward of the tool bar for transmitting such forces to the units. Therefore, the forces must be applied via the tool bar itself. At the same time, stress relief must be provided for the hitch linkages to avoid damage due to overloading within reasonably foreseeable operational circumstances.
The system of the present invention for connection of agricultural implements to the three-point hitch of a tractor is a compact system particularly suitable for tool bar type of implements where there is no long rigid frame for application of anti-pitch stabilizers and stress relief linkages. (Such implements which constitute tool bar and equivalent types sometimes are referred to herein as short frame implements, the term "short" referring to the longitudinal dimension in the direction of normal operation of the implement.) Moreover, the present system includes a resiliently yieldable means which provides resilient interconnection with high compressive force transfer capability to allow flexing and yet provide adequate orientation and attendant down-pressure forces to the tool bar when the implement is lowered for penetration of the tools into the ground.